On mini-halo encounters with stars

Abstract

We study, analytically and numerically, the energy input into dark matter mini-haloes by interactions with stars. We find that the fractional energy input in simulations of Plummer spheres agrees well with the impulse approximation for small and large impact parameters, with a rapid transition between these two regimes. Using the impulse approximation the fractional energy input at large impact parameters is fairly independent of the mass and density profile of the mini-halo, however low-mass mini-haloes experience a greater fractional energy input in close encounters. We formulate a fitting function which encodes these results and use it to estimate the disruption timescales of mini-haloes, taking into account the stellar velocity dispersion and mass distribution. For mini-haloes with mass M< {\cal O}(10^{-7} M_{\odot} on typical orbits which pass through the disc, we find that the estimated disruption timescales are independent of mini-halo mass, and are of order the age of the Milky Way. For more massive mini-haloes the estimated disruption timescales increase rapidly with increasing mass.

10 pages, 6 figures. Version to appear in MNRAS. Significant changes to presentation, but conclusions essentially unchanged